DESCRIPTION (from Abstract): Enterococci are important causative agents of a particularly serious form of bacterial endocarditis, as well as other infections. They are now among the top three nosocomial pathogens in the US. Infections caused by the enterococci are notoriously recalcitrant to antibiotic treatment, and relatively little is known about the genetic and molecular basis for the virulence of this group of bacteria. This application seeks continued support for investigation of the role of two cell wall components in enterococcal endocarditis. One component is a plasmid- encoded protein called Aggregation Substance (AS), and the second is a chromosomally-encoded factor called Enterococcal Binding Substance (EBS), which probably contains Lipoteichoic acid as its main component. AS- EBS binding is required to form a mating pair between bacterial cells undergoing conjugative plasmid transfer. Our data suggest that both AS and EBS contribute to Enterococcal Virulence in an experimental animal model of endocarditis. One or both of these compounds may also be a toxin responsible for lethality in severe cases of endocarditis. The four Specific Aims of the project listed below are designed to better define the roles of AS and EBS as virulence factors, and to identify important structure/function relationships in these molecules. SPECIFIC AIMS: 1)Determine the molecular identity of the bacterial factor responsible for lethality in severe experimental endocarditis infections. 2) Determine the mechanism by which the Toxin identified in Aim 1 causes lethality. 3) Determine the key structural features of AS and EBS required for the enhancement of virulence by these molecules. 4) Determine the mechanism by which expression of AS is induced in vivo.